Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/3217
20170224T17:21:23Z

Slow light enabled wavelength demultiplexing
http://hdl.handle.net/2117/100768
Slow light enabled wavelength demultiplexing
Hayran, Zeki; Turduev, M.; Botey Cumella, Muriel; Herrero Simon, Ramon; Staliunas, Kestutis; Kurt, H.
Photonic crystal waveguides supporting band gap guided modes hold great potential to tailor the group
velocity of propagating light. We propose and explore different wavelength demultiplexer design approaches that utilize
slow light concept. By altering the dielectric filling factors of each waveguide segment, one can show that different
frequencies can be separated and extracted at different locations along the cascaded waveguide. Furthermore, to
eliminate the inherent reflection loss of such a design, a composite structure involving a tapered waveguide with a
sidecoupled resonator is also presented. Such a structure features not only a forward propagating wave but also a
backward propagating wave acting as a feedback mechanism for the drop channels. We show that by careful design of
the waveguide and the resonator, the destructive and instructive interference of these waves can effectively eliminate
the reflection loss and increase the coupling efficiency, respectively. Numerical and experimental verification of the
proposed structures show that the targeted frequencies can be coupled out with low crosstalks and moderate quality
factors, while maintaining a compact size. © 2016 IEEE.
20170209T13:54:56Z
Hayran, Zeki
Turduev, M.
Botey Cumella, Muriel
Herrero Simon, Ramon
Staliunas, Kestutis
Kurt, H.
Photonic crystal waveguides supporting band gap guided modes hold great potential to tailor the group
velocity of propagating light. We propose and explore different wavelength demultiplexer design approaches that utilize
slow light concept. By altering the dielectric filling factors of each waveguide segment, one can show that different
frequencies can be separated and extracted at different locations along the cascaded waveguide. Furthermore, to
eliminate the inherent reflection loss of such a design, a composite structure involving a tapered waveguide with a
sidecoupled resonator is also presented. Such a structure features not only a forward propagating wave but also a
backward propagating wave acting as a feedback mechanism for the drop channels. We show that by careful design of
the waveguide and the resonator, the destructive and instructive interference of these waves can effectively eliminate
the reflection loss and increase the coupling efficiency, respectively. Numerical and experimental verification of the
proposed structures show that the targeted frequencies can be coupled out with low crosstalks and moderate quality
factors, while maintaining a compact size. © 2016 IEEE.

PTaxisymmetric photonic nanostructures
http://hdl.handle.net/2117/90240
PTaxisymmetric photonic nanostructures
Ahmed Waseem, Waqas Waseem; Botey Cumella, Muriel; Herrero Simon, Ramon; Staliunas, Kestutis
Optical ParityTime (PT) symmetric systems support unusual properties. When the symmetric coupling between internal modes is broken the system becomes strongly unidirectional resulting in novel effects such as asymmetric reflections, invisibility or asymmetric mode coupling. Here, we propose a new class of nanophotonic PTaxisymmetric systems which lead to an extreme field enhancement and high localization at the Psymmetry center when the coupling of inward propagating waves is favored due to the asymmetric radial coupling. We expect the effect to have direct applications such as rendering broad aperture lasers into bright and narrow output beam sources.
20160927T13:50:04Z
Ahmed Waseem, Waqas Waseem
Botey Cumella, Muriel
Herrero Simon, Ramon
Staliunas, Kestutis
Optical ParityTime (PT) symmetric systems support unusual properties. When the symmetric coupling between internal modes is broken the system becomes strongly unidirectional resulting in novel effects such as asymmetric reflections, invisibility or asymmetric mode coupling. Here, we propose a new class of nanophotonic PTaxisymmetric systems which lead to an extreme field enhancement and high localization at the Psymmetry center when the coupling of inward propagating waves is favored due to the asymmetric radial coupling. We expect the effect to have direct applications such as rendering broad aperture lasers into bright and narrow output beam sources.

Tunable wavelengthdemultiplexer by tapered photonic crystal waveguide
http://hdl.handle.net/2117/85665
Tunable wavelengthdemultiplexer by tapered photonic crystal waveguide
Hayran, Zeki; Turduev, Mirbek; Botey Cumella, Muriel; Herrero Simon, Ramon; Staliunas, Kestutis; Kurt, H.
We numerically investigate the design of a wavelength demultiplexer based on a tapered photonic crystal waveguide. The tapered waveguide is generated by reducing the width of the channel which, in turn, provides a gradual change in the effective index for the guided modes. Depending on the wavelength, the grading effect enables the propagating beam to be trapped at different spatial positions along the waveguide. Furthermore, alternation on the tapering angle, i.e. changing the slope of the tapered waveguide, will result in a spatial shifting of the trapping locations. Thus, the structure can be adjusted to pick up the frequencies of interest at the chosen positions. Numerical results show that, by placing vertical line defects as drop channels at specific locations, different wavelengths can be properly guided along the drop channels that are transverse to the main waveguide.
20160414T11:57:27Z
Hayran, Zeki
Turduev, Mirbek
Botey Cumella, Muriel
Herrero Simon, Ramon
Staliunas, Kestutis
Kurt, H.
We numerically investigate the design of a wavelength demultiplexer based on a tapered photonic crystal waveguide. The tapered waveguide is generated by reducing the width of the channel which, in turn, provides a gradual change in the effective index for the guided modes. Depending on the wavelength, the grading effect enables the propagating beam to be trapped at different spatial positions along the waveguide. Furthermore, alternation on the tapering angle, i.e. changing the slope of the tapered waveguide, will result in a spatial shifting of the trapping locations. Thus, the structure can be adjusted to pick up the frequencies of interest at the chosen positions. Numerical results show that, by placing vertical line defects as drop channels at specific locations, different wavelengths can be properly guided along the drop channels that are transverse to the main waveguide.

Stimulus induced resonance in a neural mass model driven with a temporally correlated noise
http://hdl.handle.net/2117/85442
Stimulus induced resonance in a neural mass model driven with a temporally correlated noise
Jedynak, Maciej; Pons Rivero, Antonio Javier; García Ojalvo, Jordi
20160408T14:43:13Z
Jedynak, Maciej
Pons Rivero, Antonio Javier
García Ojalvo, Jordi

Ultrashort pulse chirp determination via transverse autocorrelation in SBN crystal
http://hdl.handle.net/2117/84721
Ultrashort pulse chirp determination via transverse autocorrelation in SBN crystal
Wang, Bingxia; Cojocaru, Crina; Inigo Sola, Inigo Sola; Wieslaw Krolikowski, Wieslaw Krolikowski; Yan Sheng, Yan Sheng; Vilaseca Alavedra, Ramon; Trull Silvestre, José Francisco
We determine the different initial chirp parameters of ultrashort pulses down to 30 fs via singleshot transverse autocorrelation method based on transverse second harmonic generation in SBN crystal with random distribution of inverted nonlinear domains. With the measured chirp and time duration parameters, we simulate the transverse autocorrelation traces and the corresponding pulse time duration evolutions, which have a good match with the experimental results
20160318T15:19:16Z
Wang, Bingxia
Cojocaru, Crina
Inigo Sola, Inigo Sola
Wieslaw Krolikowski, Wieslaw Krolikowski
Yan Sheng, Yan Sheng
Vilaseca Alavedra, Ramon
Trull Silvestre, José Francisco
We determine the different initial chirp parameters of ultrashort pulses down to 30 fs via singleshot transverse autocorrelation method based on transverse second harmonic generation in SBN crystal with random distribution of inverted nonlinear domains. With the measured chirp and time duration parameters, we simulate the transverse autocorrelation traces and the corresponding pulse time duration evolutions, which have a good match with the experimental results

Asymmetric light transmission by using 2D PTsymmetric photonic nanostructure
http://hdl.handle.net/2117/76340
Asymmetric light transmission by using 2D PTsymmetric photonic nanostructure
Turduev, M.; Botey Cumella, Muriel; Herrero Simon, Ramon; Kurt, H.; Staliunas, Kestutis; Giden, I.
We propose for the first time a simple realization of a twodimensional ParityTime symmetric hexagonal shaped photonic structure composed of honeycomb lattice. The structure has a symmetric periodic modulation of the refractive index on the wavelength scale, which is combined with an antisymmetric gain/loss distribution on the same scale. That leads to nonreciprocal light coupling at resonant frequencies. The design of the realistic structure is based on a simple physical concept: alternating low index cylinders with gain and loss in a honeycomb configuration, embedded in a higher index dielectric background.
20150727T11:42:50Z
Turduev, M.
Botey Cumella, Muriel
Herrero Simon, Ramon
Kurt, H.
Staliunas, Kestutis
Giden, I.
We propose for the first time a simple realization of a twodimensional ParityTime symmetric hexagonal shaped photonic structure composed of honeycomb lattice. The structure has a symmetric periodic modulation of the refractive index on the wavelength scale, which is combined with an antisymmetric gain/loss distribution on the same scale. That leads to nonreciprocal light coupling at resonant frequencies. The design of the realistic structure is based on a simple physical concept: alternating low index cylinders with gain and loss in a honeycomb configuration, embedded in a higher index dielectric background.

Suppression of modulation instability by spatiotemporal modulation
http://hdl.handle.net/2117/28105
Suppression of modulation instability by spatiotemporal modulation
Staliunas, Kestutis
Modulation Instability (MI) is at the basis of spontaneous pattern formation in many nonlinear spatially extended systems in Nature, technologies, and in everyday live. In spite of variety of spatial patterns in different systems, the very onset of a spatiotemporal dynamics, the breaking of initial spatial and temporal symmetry, is initiated by MI. The said is valid for dissipative nonlinear systems, where dissipative patterns set in, but also for conservative systems. The examples in latter case ranges from the filamentation of light in Kerrnonlinear media, instabilities of Bose condensates with attractive interactions, to perhaps, the recently much discussed formation of the “rogue waves”.
20150529T15:05:10Z
Staliunas, Kestutis
Modulation Instability (MI) is at the basis of spontaneous pattern formation in many nonlinear spatially extended systems in Nature, technologies, and in everyday live. In spite of variety of spatial patterns in different systems, the very onset of a spatiotemporal dynamics, the breaking of initial spatial and temporal symmetry, is initiated by MI. The said is valid for dissipative nonlinear systems, where dissipative patterns set in, but also for conservative systems. The examples in latter case ranges from the filamentation of light in Kerrnonlinear media, instabilities of Bose condensates with attractive interactions, to perhaps, the recently much discussed formation of the “rogue waves”.

Beam focusing in chirped mirror with a defect
http://hdl.handle.net/2117/27767
Beam focusing in chirped mirror with a defect
Cheng, Yu Chieh; Staliunas, Kestutis
Recently the beam focusing in reflection from chirped dielectric mirror has been proposed and demonstrated, where the negative (anomalous) diffraction is responsible for this flat mirror focusing. For a strong focusing performance (large focal distance), a wide angular range of strong (negative) angular dispersion is required. We show that a defect layer in the dielectric mirror (one layer is of a double size), can increase the angular dispersion, and thus improve the focusing performance. By introducing a defect layer in the chirped mirror, the focal distances can be increase from 12 µm up to 22 µm in a specific, calculated, structure, as our numerical integration show.
20150506T09:53:50Z
Cheng, Yu Chieh
Staliunas, Kestutis
Recently the beam focusing in reflection from chirped dielectric mirror has been proposed and demonstrated, where the negative (anomalous) diffraction is responsible for this flat mirror focusing. For a strong focusing performance (large focal distance), a wide angular range of strong (negative) angular dispersion is required. We show that a defect layer in the dielectric mirror (one layer is of a double size), can increase the angular dispersion, and thus improve the focusing performance. By introducing a defect layer in the chirped mirror, the focal distances can be increase from 12 µm up to 22 µm in a specific, calculated, structure, as our numerical integration show.

Excitation/inhibition patterns in a system of coupled cortical columns
http://hdl.handle.net/2117/27684
Excitation/inhibition patterns in a system of coupled cortical columns
Malagarriga Guasch, Daniel; Villa, Alessandro; García Ojalvo, Jordi; Pons Rivero, Antonio Javier
We study how excitation and inhibition are distributed mesoscopically in small brain regions, by means of a computational model of coupled cortical columns described by neural mass models. Two cortical columns coupled bidirectionally through both excitatory and inhibitory connections can spontaneously organize in a regime in which one of the columns is purely excitatory and the other is purely inhibitory, provided the excitatory and inhibitory coupling strengths are adequately tuned. We also study the case of three columns in different coupling configurations (linear array and alltoall coupling), finding abrupt transitions between heterogeneous and homogeneous excitatory/inhibitory patterns and strong multistability in their distribution.
20150430T08:53:32Z
Malagarriga Guasch, Daniel
Villa, Alessandro
García Ojalvo, Jordi
Pons Rivero, Antonio Javier
We study how excitation and inhibition are distributed mesoscopically in small brain regions, by means of a computational model of coupled cortical columns described by neural mass models. Two cortical columns coupled bidirectionally through both excitatory and inhibitory connections can spontaneously organize in a regime in which one of the columns is purely excitatory and the other is purely inhibitory, provided the excitatory and inhibitory coupling strengths are adequately tuned. We also study the case of three columns in different coupling configurations (linear array and alltoall coupling), finding abrupt transitions between heterogeneous and homogeneous excitatory/inhibitory patterns and strong multistability in their distribution.

Beam focalization by chirped mirrors
http://hdl.handle.net/2117/27289
Beam focalization by chirped mirrors
Cheng, Yu Chieh; Peckus, Martynas; Kicas, Simonas; Trull Silvestre, José Francisco; Cojocaru, Crina; Vilaseca Alavedra, Ramon; Drazdys, Ramutis; Staliunas, Kestutis
A novel application of chirped dielectric mirrors for narrow beam focalization is proposed and demonstrated numerically and experimentally. Analogy to temporal dispersion compensation by chirped dielectric mirrors is discussed.
20150413T14:59:48Z
Cheng, Yu Chieh
Peckus, Martynas
Kicas, Simonas
Trull Silvestre, José Francisco
Cojocaru, Crina
Vilaseca Alavedra, Ramon
Drazdys, Ramutis
Staliunas, Kestutis
A novel application of chirped dielectric mirrors for narrow beam focalization is proposed and demonstrated numerically and experimentally. Analogy to temporal dispersion compensation by chirped dielectric mirrors is discussed.